Flow of Ground Water. 



269 



in cubic feet per minute per square foot of section and per 

 foot of length, under a gradient of 1 in 10, is given below : 



No. 8 7 

 Cu. ft. per min. 5.23 3. 65 



6 



1.85 



1.36 



5 

 1.22 



4 



.82 



3 

 .51 



2 1 

 .33 .23 .18 



Fio. 99. Apparatus -for measuring the flow of water through sandstones, 

 under different known pressures. 



According to Darcy's law, if these sand columns had their 

 lengths increased 10, 100 and 1,000 times the discharges 

 observed would be only iV, iU and 7o\>o of those given. 

 In the case of four sandstones the rates of flow were so slow 

 that 10 days were required for .29, .34, 2.45 and .14 cubic 



